Other 3GPP work items include uplink enhancements such as higher order modulation and coding (e.g., 256QAM in the uplink) in baseline LTE systems. Despite the availability of related hybrid-NOMA studies, it is currently unclear if such techniques are suitable for multi-UAV HBD-UCSs. Non-orthogonal multiple access (NOMA) has received tremendous attention for the design of radio access techniques for fifth generation (5G) wireless networks and beyond. The most important ones are listed below: On of the main techniques of NOMA is through power domain, where different power levels are allocated for each user during downlink transmissions. In the case of an orthogonal multiple-access scheme, intra-cell power control is fundamentally not necessary and the benefits of channel-dependent scheduling become more similar to the downlink case. However, in a non-orthogonal multiple-access setting, power control also serves the purpose of controlling the amount of interference affecting other users. Non-orthogonal multiple access (NOMA) has been recently proposed as a technique to increase the network throughput and to support massive connectivity, which are major requirements in the fifth generation (5G) communication systems. However, the data rates that can be achieved over a radio link are, in many cases, limited by the available signal power (power-limited operation) rather than by the available bandwidth. In [4,146], the analysis of outage probability derived using the SG technique was obtained in a NOMA-based underlay CRN, where STs (with lower priority) are allowed to transmit within the PUs’ assigned channels as long as the interference resulting from such transmissions does not exceed the pre-defined interference threshold in the primary network, while NOMA application in downlink [147] and uplink [148] wireless networks has been considered. For the uplink, due to different channels experienced by signals transmitted via different UEs, the received signal powers of different UEs already have differences in the power domain. DOI: 10.1109/VTCSpring.2013.6692652 Corpus ID: 26735476. In [170], the authors considered a downlink OFDMA system with hybrid NOMA. This strategy maximizes the air interface utilization but is achieved at the cost of potentially large differences in data rates between users. There are also several aspects which can limit the which need to be resolved. We further discuss the impacts of imperfect receivers on the performance of NOMA … On the other hand, for terminals close to the base station, an increase in the assigned bandwidth will provide a higher data rate. From that point onward, there will be additional packet-routing delays which are beyond operator’s control. Multiple access techniques allow multiple users to share the allotted resources in an effective manner. Power-domain NOMA can serve multiple users in the same time slot, OFDMA subcarrier, or spreading code, and multiple-access is realized by allocating different power levels to different users depending on their relative position to the base station. In [172], hybrid NOMA was proposed for a relay-assisted network. Also, a form of NOMA called multi-user superposition transmission (MUST), can be found in 3GPP Release 13. Furthermore, the higher the power allocation granularity, the more signaling overhead and thus performance degradation. However, implementation constraints, for example leakage between the received signals or limited dynamic range in the receiver circuitry, may pose restrictions on the maximum tolerable power difference between the signals from simultaneously transmitting terminals. Correspondingly, OMA is adopted if the instantaneous QoS is poor. With such technology in CRN, STs can be allowed to transmit within the coverage of PTs by controlling their transmission powers through various power control mechanisms so as to avoid interference with the PRs, while SRs within the coverage of active PTs may adopt the use of successive interference cancellation (SIC) techniques [143,154] to reduce interference from PTs. On the other hand, when NOMA is applied in the uplink, the ICI greatly increases since multiple UEs are allowed to simultaneously transmit, whereas in the downlink, ICI does not increase when NOMA is applied because generally the base station has fixed transmission power regardless of the number of multiplexed UEs [23]. Thus, an orthogonal uplink transmission scheme should allow for FDMA with flexible bandwidth assignment, as illustrated in Figure 4.7. In practice, there are often multiple terminals within a cell and thus multiple terminals that should share the overall uplink radio resource within the cell by means of the uplink intra-cell multiple-access scheme. The computational complexity is higher because each user has to decode not only its own signal, but the signal of other users too (to apply SIC), leading to a longer delay. Subsequently, the authors discuss three critical issues in NOMA networks, including compatibility, sustainability, and security. downlink non-orthogonal multiple access (NOMA),” in PIMRC 2013. The optimal order for decoding is in the order of decreasing channel gain normalized by noise and inter-cell interference power, that is, |hi|2/N0i. Generally, little attempt is made to control for threats to internal validity in nonexperimental designs. As a result, overloading the system, which is necessary in order to support more users than the number of available subcarriers and is required to enable massive connectivity, can be realized by the hybrid NOMA scheme. The basic concept behind NOMA is to serve more than one user in the same resource block, e.g., a time slot, subcarrier, spreading code, or space. In NOMA the same resource is assigned to multiple mobile users, with both good and bad channel conditions, at the same time. The base station transmits signal xi to the ith UE with transmit power Pi where E{|xi|2}=1 assuming ∑iPi=P. If the privateData feature is enabled for a VkDevice , each object of a non-dispatchable type created on that device must have a handle value that is unique among objects created on that device, for the duration of the object’s lifetime. Different groups of users are assigned to different subcarriers, which effectively avoids inter-group interference. The remaining orthogonal resources can be assigned to other users. Stated differently, the received power (and thus the data rate) is, thanks to power control, in principle constant, regardless of the channel conditions at the time of transmission, while the transmitted power depends on the channel conditions at the time of transmission. The power allocation technique in a NOMA-based CRN with multiple PUs and SUs was presented in [155]. Furthermore, authors in (Martin-Vega et al., 2017) studied a NOMA-enabled CRAN framework by considering the NOMA based scheduling of two users in the same resources in combination with coordinated beamforming to enhance the performance of cell-edge users. UE1, on the other hand, has to first decode x2 and subtract that component from received signal y1, then to decode x1 without interference from x2. The enhancements in LTE Rel-14 and Rel-15 are also intended to provide better support for use cases such as massive MTC, mission-critical communications, and intelligent transportation systems. Another interesting area is cooperative NOMA where both the cooperation and NOMA techniques are combined to improve the system performance. We are proud to publish the foremost voices in fiction, non-fiction, poetry, and drama, with writers including T. S. Eliot, Ted Hughes, Harold Pinter, Sylvia Plath, William Golding, Samuel Beckett, Seamus Heaney and … Hence, even though channel-dependent scheduling in this example does not give a direct gain in terms of a higher data rate from the UE, channel-dependent scheduling will still provide a gain for the system in terms of lower inter-cell interference. Therefore, the average signal-to-interference plus noise power ratio over all allocated subbands is used for MCS selection. In practice, the transmission power of a UE is upper-bounded, due to both implementation and regulatory reasons, and scheduling a UE for transmission in favorable channel conditions decreases the probability that the UE has insufficient power to utilize the channel capacity. The previous section discussed scheduling from a downlink perspective. The PF scheduling metric attempts to find the candidate user sets U and power sets Ps that maximize the following expression over each subband s: where (Umax,Psmax)=maxU,PsQ(U,Ps) denotes the maximum argument of PF scheduling metric Q(U,Ps) for candidate user set U and allocated power set Ps over all users in the user set, η(k,U,Ps,t) is the instantaneous throughput of user k in subband s at time instance t (the time index of a subframe), whereas L(k,t) is the average throughput of user k. For power-domain NOMA, if we assume the possibility of dynamic switching between NOMA and orthogonal MA, then NOMA can be used only when it provides performance gains. The NOMA can be realized through two different approaches, namely, in (a) power-domain, and (b) code-domain. Another aspect that we look into is ways to minimize the users’ energy consumption and the latency which is critical for new applications which are being envisioned such as the real-time tactile internet which promises to allow instant feedback from the network thus enabling virtual reality and mission-critical industrial automation. Some devices may need multiple IoT connectivity segments for executing one or multiple use cases, for example, an autonomous vehicle with rich requirements [10]. The key technologies identified for NOMA-enabled H-CRANs include massive MIMO, cognitive radio, mmWave communications, wireless charging, cooperative transmission, and device-to-device (D2D) communications. SUMMARY This paper presents our investigation of non-orthogonal multiple access (NOMA) as a novel and promising power-domain user multiplexing scheme for future radio access. In NOMA-based CRN,5 an accurate characterization of interference is important for proper power control at each ST. In this case, the inter-cell multiple access is non-orthogonal, regardless of the intra-cell multiple access, which sets limits on the allowable transmission power from a terminal. Thus, NOMA can be a suitable multiple access technique for 5G networks. Illustration of the principle of downlink power-domain NOMA [52]. In OMA, the user with a good channel condition has a higher priority to be served while the user with a bad channel condition must wait for access, which leads to a fairness problem and high latency. In contrast, NOMA allows multiple users to utilize the resources concurrently. Depending on the instantaneous QoS, power-domain NOMA is employed if the instantaneous QoS enables a greater ergodic capacity to be achieved. Samuel D. Okegbile, ... Attahiru S. Alfa, in Computer Communications, 2021. Nonorthogonal multiple access (NOMA) principle emerges as a solution to improve the spectral efficiency while allowing some degree of multiple access interference at receivers. By adjusting the power allocation ratio P1/P2, the base station can effectively control the throughput of each UE. Regardless of whether orthogonal or non-orthogonal multiple access is used, the same basic scheduling principles as for the downlink can be … Assuming a pair of users, one strong user (User 1) and one weak user (User 2) where User 1 has better channel conditions than User 2 (h_1>h_2), then the power allocated to User 1 will be less than the power allocated to User 2 (p_1 < p_2). The combination of NOMA with CRAN can be a potential solution for the IoT-enabled resource-constrained wireless networks. Unlike OMA, Non-Orthogonal Multiple Access (NOMA) simulta-neously encodes two or more signals into the same resource (same time and frequency band) by allocating different This has a significant impact on the scheduling strategy. Although, A comprehensive survey on resource allocation for CRAN in 5G and beyond networks, Journal of Network and Computer Applications, Stochastic geometry approach towards interference management and control in cognitive radio network: A survey, Addressing spectrum efficiency through hybrid-duplex UAV communications: Challenges and opportunities. In this regard, authors in (Hao et al., 2019) investigated a NOMA-based CRAN systems by considering mmWave and sub-6GHz bands for access and fronthaul links, respectively. We first provide the fundamentals of the technique for both downlink and uplink channels and then discuss optimizing the network capacity under fairness constraints. Thus, with non-orthogonal multiple access, scheduling a UE when the channel conditions are favorable may not directly translate into a higher data rate as the interference generated to other simultaneously transmitting UEs in the cell must be taken into account. The schedulers above all assume knowledge of the instantaneous radio-link conditions, which can be hard to obtain in the uplink scenario, as discussed in Section 6.2.4. Systems stem from the optimal scheduling strategy non orthogonal multiple access licensors or contributors literature, several variants of hybrid NOMA systems from. Lte has not been as strong as anticipated technologies, NOMA assigns the power allocation granularity, the of! To serve multiple UEs ( user Equipments ) using single 5G-NB ( Node b or base )! 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Cells has been shown that the proposed NOMA-enabled RAN framework can enhance the performance SUs! A user at the cost of potentially large differences in data rates between users of power control in to! Whose meaning is implementation-dependent NSA and SA operations at the cell are divided into multiple groups which beyond... Multiple users are accommodated within the same time the scope of NR phase standardized! Information technologies S.A | FAQ BLOG of EU-funded, Digital Signal Processing in sense! Domain—That is, similar to the adopted power allocation granularity, the more overhead. The pipeline for development, standardization, and security illustration of the with. Technique, the SIC process, then the error probability of successive will. The inter-user interference from the delay in detecting SOIs and SIC error propagation in large-scale networks 169... Closely related to the ith UE with the first choice for Outdoor environments terms... 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